Structure and method of assembly of bearing support means to the stator assembly of an electric motor

ABSTRACT

An electric motor structure and method of assembling the same wherein such structure includes a laminated stator core with a rotor body disposed therein with a rotor shaft extending therefrom to be supported by bearing support end shield means having bearing supports tightly fastened to said stator core in a manner that resistance to bending forces is less in the laminated stator core than the resistances to bending forces of the bearing support end shield means to enhance stability and squareness of the bearing support end shield means and bearing supports of the motor assembly.

BACKGROUND OF THE INVENTION

This invention relates to an improved electric motor structure andmethod of assembling the same and more particularly to an improvedstructure and method for securing a bearing support end shield to thestator assembly of an electric motor, for example, a fractionalhorsepower electric motor.

An electric motor, such as a fractional horsepower motor known in theart, generally includes a stator assembly of a stack of laminations(preferably made of sheets of suitable steel or other ferro-magneticmaterial) punched or stamped with a central bore and a plurality ofwinding receiving slots extending generally radially outwardly from thebore. The laminations are stacked to form a stator core and securedtogether in one or more of several ways including welding, epoxyadhesive and fastener cleats. A rotor assembly including a rotor bodyand an axial shaft extending therefrom is centered in the central boreof the stator core with a uniform air gap therebetween with the rotorshaft extending centrally from the rotor body end. Bearing support endshield means is secured to the stator assembly so that the rotor shaftis rotatably journalled in the bearing support to rotatably support therotor body within the stator core assembly.

A number of assembly structures for securing the bearing support endshield means to the stator assembly have been employed in the art. Themore recently issued U.S. Pat. No. 4,306,168 and No. 4,361,953 to C.Theodore Peachee on Dec. 15, 1981 and Dec. 7, 1982, respectively teach anovel apparatus and method for securing bearing support end shields tothe stator assembly of an electric motor by utilizing self-tappingscrews and removable shims during assembly operations.

The present invention, recognizing the advantageous features taught bythese aforementioned patents, as well as certain of the limitations,provides an improved apparatus and method for securing bearing supportend shield means to the stator core assembly of an electric motor whichutilizes such past advantageous features combined with unique and noveladditional structural features and method steps, which new structure andsteps are low in cost in manufacture and assembly and which furtherenhance structural stability and balanced support of an assembledelectric motor without special parts or expensive, complex processingsteps and without jeopardizing the overall strength of the electricmotor. In accordance with the present invention, a novel electric motoris provided which not only is economical in manufacture and assembly,but which is sturdy and stable with enhanced squareness and balancenecessary for the rotor shaft ball bearings when operated under highloads and/or high speeds so as to extend motor life. This enhancedsquareness is obtained in an economical and straightforward structureand method substantially less complex than past arrangements forsquaring rotor shaft ball bearings.

Various other features of the present invention will become obvious toone skilled in the art upon reading the disclosure set forth herein.

SUMMARY OF THE INVENTION

More particularly the present invention provides an electric motorcomprising a stator assembly including a stator core assembled from astack of core laminations, the stator core having a central boreextending longitudinally therethrough and a plurality of core holes inthe core surrounding the bore with core hole openings thereof along theend faces of the stator core; a rotor assembly including a rotor bodycentered within the bore, the rotor body having a rotor shaft extendingendwise therefrom; bearing support end shield means having bearingsupports for reception and journalling of the rotor shaft to rotatablysupport the rotor assembly within the central bore of the stator core,the bearing support end shield means including a plurality of bearingsupport end shield openings therein in register with the core holeopenings; a plurality of fasteners extending through the registeredbearing support end shield means openings and core hole openings intothe core holes to tightly draw the bearing support end shield means intofirm engagement with the stator core; and lamination joining meansarranged to firmly grip and hold together the stack of laminations ofthe stator core, the lamination joining means being preselected toprovide resistance to the bending moment along a preselected distance inthe laminations created by the tightening of the plurality of fastenersto be less than the resistance to the bending moment along a distance inthe bearing support end shield means whereby the bearing supports in thebearing support end shield means are maintained in squared, stableposition relative the rotor shaft with any bending created by fastenertightening forces occurring among the stack of laminations of the statorcore rather than the bearing supports in the bearing support end shieldmeans to insure assembled stability of the bearing support end shieldmeans and bearing supports. Further, the present invention provides in amethod of assembling an electric motor having a stator assemblyincluding a core made up of a stack of laminations of suitable magneticmaterial, the core having joining means to firmly grip and hold togetherthe stack of laminations, a central bore extending therethrough, a rotorassembly including a rotor body adapted to be rotatably received in thebore and a rotor shaft extending endwise from the rotor body, and atleast one bearing support end shield, the bearing support end shieldhaving a bearing support to receive and journal the rotor shaft, thesteps comprising: forming holes in the core and the bearing support endshield in register with each other; inserting the rotor assembly intothe stator assembly with the rotor being received in the bore; centeringthe rotor body within the bore with an air gap between body and core ofsubstantially uniform thickness therearound; installing the bearingsupport end shield on the stator and rotor assemblies with the rotorshaft journalled in the bearing support and the bearing support endshield bearing against an adjacent lamination of the core withregistered core and bearing support end shield holes aligned; insertingfasteners through the aligned holes to be tightened to draw the bearingsupport end shield into firm gripping engagement with the core; thejoining means for the core laminations being preselected so thatresistance to bending moment created along a preselected distance of thelaminations when the fasteners are tightened is less than the resistanceto the bending moment created along a distance on the bearing supportend shield between the fastener and the bearing support on the endshield to maintain the bearing support of the bearing support end shieldin stable, squared position with any bending moment created by fastenertightening occurring among the stack of laminations of the core ratherthan the bearing support end shield and bearing support. In addition,the present invention employs, in combination with the aforegoing, aself-tapping screw arrangement with the holes in the bearing support endshield being sized to accommodate a portion of the material from outwardcore laminations during fastener tightening to further squarely securethe bearing support end shield in place with respect to the core andalso employs the use of shims in the centering of the rotor body in thestator core.

It is to be understood that various changes can be made by one skilledin the art in one or more of the several parts of the electric motorapparatus disclosed herein and in one or more of the several steps ofthe disclosed method without departing from the scope or spirit of thepresent invention. For example, joining of stator core laminations canbe accomplished in other ways besides with the joining cleats disclosed,the stator core and bearing support end shield structure can be variedmechanically and geometrically, as can the relative thickness andmaterials of the stator core laminations and bearing support endshields - care being taken to control the relative resistance to bendingmoment between these several parts to fall within the inventive scope ofthis disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which disclose one advantageous embodiment ofthe invention:

FIG. 1 a side view of an electric motor structure including a statorcore assembly and a bearing support end shield means incorporating theinventive features and disclosing in somewhat exaggerated form theeffects of the controlled resistance to bending moment of the severalparts;

FIG. 2 is a top plan view or one of two opposed end faces of the statorcore of stacked assembly of laminations, disclosing the relativepositioning of stator core holes and notched core laminations;

FIG. 3 is an exploded side view of the several parts of the motor ofFIG. 1, further disclosing in broken line form shims used in theassembly thereof the position of the rotor relative the stator core andthe pillow block and bearing in each end shield; and,

FIG. 4 is a view similar to that of FIG. 1, also disclosing in somewhatexaggerated form the possible effects of uncontrolled resistance tobending moment of the several parts.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1, 3 and 4 of the drawings, there is disclosed adynamo-electric machine in the form of a fractional horsepower electricmotor 2. Motor 2 includes a stator assembly 3, a rotor body assembly 4and a pair of opposed bearing support end shields 6 and 7 secured to thestator assembly 3 for journalling the rotor shaft 8 or rotor assembly 4into bearing supports 9 on opposed end shields 6 and 7, Each bearingsupport 9 includes a pillow block 10 for an anti-friction bearing 10'sized to receive a corresponding end of rotor shaft 8. Motor 2 may beany conventional electric motor or other dynamo-electric machine. Thestator assembly 3 is composed of a stator core 11 made up of a pluralityof similar laminations 12 arranged in a stack (FIG. 2). Each lamination12 advantageously is a stamped or punched plate-like member having acentral opening to provide bore 13. A plurality of winding slots 14(FIG.) extends radially outward from bore 13 to receive and retainstator windings of stator assembly 3. The laminations are made of asuitable magnetic material, advantageously of sheet steel or othersuitable ferro-magnetic material. The laminations 12, which can bestamped in any one of a number of geometric configurations,advantageously are disclosed as a rectangular square in the present formof the invention.

As can be seen in FIG. 2 of the drawings, each lamination 12 is providedwith holes at the corners which when aligned upon stacking to formstator core 11 serve to form core holes 17 extending through the statorcore 11 with openings along opposite end faces of the core. Inaccordance with the advantageous embodiment of the present inventiondisclosed, each lamination 12 is notched along the periphery apreselected distance from each hole formed therein so that cleat notches18 are formed in the peripheral sides of stator core 11 when thelaminations 12 are stacked to form stator core 11, each of these cleatnotches 18 being a preselected distance from a core hole 17 for reasonsdescribed hereinafter. As disclosed, each cleat notch 18 is of rightangular contour of a size sufficient to accommodate a U-shaped joinercleat 19 with its base leg extending longitudinally along the side faceof the stack of laminations forming a stator core 11 with thelongitudinal axis thereof preselectively spaced from and parallel thelongitudinal axis of an adjacent core hole 17. The spaced opposite sideor end legs, of each joiner cleat 19 grip the opposed outsidelaminations at the opposed end faces of stator core 11 and the stack oflaminations therebetween to firmly secure together the stackedlaminations of the stator core 11. It is to be understood that thepresent invention is not to be considered as limited to the specificjoiner cleat disclosed but that other types of lamination joiningarrangements can be employed to accomplish the purposes of theinvention. As known in the electric motor art, rotor assembly 4, whichincludes a rotor body (not shown in detail) is centered within bore 13of stator core 11, the rotor assembly 4 further including central rotorshaft 8 extending therefrom which has mounted thereon radial bladedmotor fan 21 (FIGS. 1 and 3), which four 21 can include as known in theart, a central hub portion (not shown) which can be appropriately pressfitted or spliced to shaft 8.

Referring to FIG. 3 of the drawings, it can be seen that bearing supportend shields 6 and 7, abovenoted as being secured to stator assembly 3for journalling and supporting the rotor shaft 8 of rotor assembly 4into bearing supports 9, includes a plurality of bearing support endshield openings 22 in each bearing support end shield at the cornersthereof positioned to be in register with the openings of core holes 17in stator assembly 3. As disclosed in detail the aforenoted U.S. Pat.Nos. 4,306,168 and 4,361,953 and therefore not disclosed in thedrawings, these bearings support end shield openings 22 are larger thanthe registered openings of core holes 17, being of sufficient size sothat at least the outermost core lamination adjacent a core hole openingof a core hole 17 protrudes into the registered bearing support endshield opening 22 when the core lamination is bent into such opening bytightening of the fasteners inserted through the registered openingsinto a core hole 17. In this regard, in a similar manner as alsodisclosed in the above U.S. Pat. Nos. 4,306,168 and 4,361,953, aplurality of threaded self-tapping fasteners 23 is utilized to extendthrough registered support openings 22 and the openings of core holes 17to be tightened in the core holes. Pursuant to the advantageousembodiment of the present invention as disclosed, the aforenotedpreselected distance from a self-tapping fastener 23 and thelongitudinal axis of the base leg of a U-shaped joining cleat 19 is suchthat the resistance to the bending moment created by the forcetightening of self-tapping screw 23 is less than the resistance to thebending moment created along a distance on an adjacent bearing supportend shield between self-tapping fastener screw 23 and a bearing support9 on the bearing support end shield. As a consequence of this differenceof resistance to bending moment, the bearing supports on bearing supportend shields 6 and 7 are maintained in squared position relative rotorshaft 8 with any bending created by the tightening forces ofself-tapping screws 23 occurring among stacked laminations 12 of rotorassembly 3, as disclosed in exaggerated form by reference numeral 24 inFIG. 1, rather than the bearing supports of bearing support end shieldsto assure assembly stability of such bearing supports in their bearingsupport end shields.

Again referring to FIG. 3 of the drawings, in carrying out the severalsteps of the inventive method of assembling the several parts of thenovel electric motor described herein, the laminations 12 of suitablemagnetic material are each stamped or punched as square rectangles toinclude a large central opening with radially extending, winding slots,four corner openings and four peripheral notches, each spaced apreselected distance from an adjacent corner opening. The laminations 12are then stacked to form stator assembly 3 including a stator corehaving a central bore 13, four corner core holes 17 with four joiningcleat peripheral notches 18, each notch 18 being preselectively spacedfrom its adjacent core hole 17. U-shaped lamination joining cleats 19are then inserted into cleat notches 18 with the base legs of the cleats19 extending along the side wall of the stator core assembly 3 and theside legs of cleats 19 gripping laminations 12 therebetween. Once statorwindings 16 are wound in winding slots 14 of stator core 11 (FIG. 2) ina manner in the art, the rotor body of rotor assembly 4 is centered incentral bore 13 of stator core 11 (FIG. 2) of stator assembly 3 (FIG. 3)by installing shims 26 (shown in broken lines in FIG. 3) between therotor body and the inner wall of the stator core defining central bore13. With this accomplished, the bearing support end shields 6 and 7 areassembled on opposed faces of the stator core 11 of the stator assembly4 with bearing supports 9 receiving and journalling the rotor shaft 8extending from opposed faces of the rotor body of rotor assembly 4 andwith bearing support end shield openings or holes 22 larger than andregistering with core holes 17.

Self-tapping fastener screws 23 are then inserted into the registeredopenings 22 and core holes 17 and tightened to a preselected torque.Referring to FIG. 1 of the drawings, since the preselected distancesbetween adjacent screws 23 and lamination joining cleats 19 are suchthat resistance to the bending moment created along each of thepreselected distances between screw and cleat when the screw istightened is less than the resistance to the bending moment createdalong a distance on the associated bearing support end shield betweenthe screw and the bearing support, the bearing support end shield andbearing support thereon are maintained in stable square position as canbe seen in FIG. 1. As also can be seen in FIG. 1 in exaggerated form asdesignated by reference numeral 24, any bending moment created by thetorquing forces of tightened screws 23 occurs among the stack oflaminations 12 of stator core 11. As the laminations bend in accordancewith the novel relative resistance to bending moment forces in theinventive structure described, the portion of the material from outwardlaminations of the core is accommodated by the large registered bearingsupport end shield holes 22 to further squarely secure the bearingsupport end shields in place with respect to the stator core. At thisjuncture in the method, shims 26 are then removed from the space betweenthe inner wall of the stator core and the rotor body.

Referring to FIG. 4 of the drawings, an undesirable condition isdisclosed by the exaggerated dotted lines indicated by reference numeral27, such condition involving the possible bending of the bearing supportend shield because of the changed close spacing of cleats 19 relativecore holes 17 and self-tapping screws 23 so that the resistance tobending moment has been reversed - namely that of the bearing supportend shield is less than the joined laminations with the tighteningtorque causing the end shield to bend rather than the limitations. Sucha situation results in lack of motor squareness, concomitant bearingsupport squareness and alignment and possible binding of the severalparts upon operation.

The invention claimed is:
 1. An electric motor comprising: a statorassembly including a stator core formed and assembled from a stack ofcore laminations, said stator core formed and assembled from said stackof core laminations having a central bore extending longitudinallytherethrough and a plurality of spaced core holes in said coresurrounding said bore with said core holes having openings therein alongthe opposed end faces of said stator core;a rotor assembly including arotor body centered within said bore, said rotor body having a rotorshaft extending endwise therefrom; bearing support end shield meanshaving bearing supports for reception and journalling of said rotorshaft to rotatably support said rotor assembly within said central boreof said stator core, said bearing support end shield means including aplurality of bearing support end shield openings therein spaced to be inalignment with and in register with said core hole openings of said coreholes surrounding said central bore of said stator core; a plurality offasteners extending through said spaced and aligned registered bearingsupport end shield means and core hole openings into said core holes ofsaid stator core to tightly draw said bearing support end shield meansinto firm engagement with said stator core; and, core lamination joiningmeans arranged to firmly grip and hold together said assembled stack ofcore laminations forming said stator core, said core lamination joiningmeans being preselected in spaced position relative to said fasteners toprovide resistance along said stack of assembled core laminations to thebending moment created by the tightening of said plurality of fastenersextending into said core holes of said stator core to be less than theresistance to the bending moment along said bearing support end shieldmeans whereby said bearing support end shield means is maintained insquared stable position relative said rotor shaft with any bendingcreated by fastener tightening forces occurring among the stack ofassembled laminations forming said stator core rather than the bearingsupport end shield means to insure assembled stability of the bearingsupport end shield means.
 2. The electric motor of claim 1, said bearingsupport end shield means spaced openings in alignment with and inregister with said core hole openings, each being of sufficient size sothat at least the outermost core lamination adjacent a core hole openingprotrudes into said aligned and registered bearing support end shieldopening when said core lamination is bent into the mating aligned andregistered bearing support end shield opening to enhance stator assemblystability.
 3. The electric motor of claim 1, said stack of corelaminations assembled to form said stator core having aligned notchesadjacent the peripheral edges thereof to form notches in said statorcore extending between said opposed end faces of said stator core, saidnotches being spaced a preselected distance from adjacent fastenersextending into said core holes to nestingly receive said laminationjoining means.
 4. The electric motor of claim 1, said lamination joiningmeans being cleats spaced a preselected distance from adjacentfasteners, each cleat being of U-shape contour with the base leg of eachcleat extending longitudinally along the peripheral side face betweensaid opposed end faces of said stack of core laminations forming saidstator core with the space opposite end legs of each clip gripping theopposed outside laminations determining said opposed end faces of saidstator core and the stack of assembled laminations therebetween, all ofwhich form said assembled stator core.
 5. The electric motor of claim 1,said stack of core laminations assembled to form said stator core, eachbeing of substantially rectangular shape with said spaced, aligned andregistered mating bearing support end shield openings and core holeopenings being positioned adjacent the corners of said stator core. 6.The electric motor of claim 1, said fasteners being threaded screwssized to threadedly engage in mating relation with said core holes. 7.An electric motor comprising:a stator assembly including a stator coreassembled from a stack of square core laminations of suitable magneticmaterial, said stator core assembled from said core laminations having acentral bore extending longitudinally therethrough and a plurality ofspaced core holes positioned adjacent the corners of said assembledstator core with the core hole openings of said core holes being alongthe opposed end faces of said stator core, said stack of squarelaminations having spaced cleat notches adjacent the peripheral edgesthereof to form spaced longitudinally extending notches in theperipheral side face of said stator core extending between said opposedend faces of said stator core, each longitudinally extending notch beingpreselectively spaced from one of said core hole openings; a rotorassembly including a rotor body centered within said bore; said rotorbody having a rotor shaft extending endwise therefrom; opposed bearingsupport end shields having bearing supports for reception andjournalling of said rotor shaft to rotatably support said rotor assemblywithin said central bore of said stator, said end shield including aplurality of bearing support end shield openings at the corners thereofto be aligned with and in register with said core hole openings of saidassembled stator core, said bearing support end shield openings eachbeing of sufficient size so that at least the outermost core laminationadjacent a core hole opening protrudes into said aligned and registeredbearing support end shield opening when said core lamination is bentinto the mating bearing support end shield opening to enhance statorassembly stability; a plurality of threaded self-tapping fastener screwsextending through said aligned and registered bearing support end shieldand core hold openings into threaded engagement with said core holes totightly draw said bearing support end shields into firm engagement withsaid stator core; and, a plurality of spaced U-shaped joiner cleats withtheir base legs extending longitudinally along said peripheral side faceof said stator core between said opposed end faces thereof said stack ofcore laminations and the spaced opposite side legs of each cleatgripping the opposed outside laminations and the stack of laminationstherebetween, the longitudinal axis of each cleat base leg being spaceda preselected distance from an adjacent fastener screw to provideresistance to the bending moment created along such preselected distancebetween such fastener screw and said cleat when said fastener screw isforce tightened which resistance is less than the resistance to thebending moment created along a distance on an adjacent bearing supportend shield between such fastener screw and said bearing support on saidbearing support end shield whereby said bearing support is maintained insquared position relative said rotor shaft with any bending created byfastener screw tightening forces occurring among the stack oflaminations of said core rather than the bearing support end shield toassure assembled stability of the bearing support shield and bearingsupport.